A thread-delivery device is known from U.S. Pat. No. 4,027,505. Its thread-control element has two approximately parallel lever arms which are arranged pivotal about a common axis such that their free ends, which are provided with eyelets, extend on both sides of a thread-guiding roller. A spring engages, at a position spaced from the swivel axis, one of the lever arms such that it urges the lever arms in a position in which the eyelets and thus the thread guided through them are in the delivery-belt-free area of the thread roller. The same lever is extended beyond the swivel bearing, and a pull rope is secured on it at one end, the other end of which is connected to a rocking lever in the area of the control system of the knitting machine. The rocking lever is moved into two different end positions through a mechanism by the control members for the needles, depending on whether threads are, or are not, being supplied by the respective system. In the case of thread supply, the rocking lever tensions the pull rope such that it maintains the lever arms of the thread-control element against the force of the spring in a position in which the eyelets are at the level of the delivery belt on the thread roller. During paying out of the thread the rocking lever changes position, whereby the pull rope becomes loose and the spring can relax, so that the thread can move out of the area of the delivery belt, and the thread delivery is interrupted. If thread again is consumed at the respective system, the rocking lever tensions the pull rope and the thread delivery starts again. This known device uses expensive mechanical means. Futhermore the pull ropes, which extend from the thread rollers which are arranged above the working area to the control members which are stored below the working area of the knitting machine, make the working area itself difficult to reach. To monitor thread breakages, an additional thread-breakage monitor as a separate structural part must be arranged to turn off the knitting machine. After the machine has been turned off, thread is still being supplied as long as the delivery belt continues to run due to the inertia of its drive mechanisms. In so far as we are dealing with a turning-off means of a common type, which reacts to a change in the thread tension, it must furthermore differentiate whether it is dealing only with a tension drop during a thread change or indeed with a thread breakage.
Should the thread monitoring occur with one single member, same must interrupt the positive thread delivery during paying out and clamping of the thread, and must stop the machine during thread breakage. If one uses for this a common turning-off means, then same would have to run through a very large swivel path and interrupt the delivery after a first small angle, and stop same after a substantially larger angle. In order to be able to carry out the interruption of the delivery during paying out of the thread as quickly as it is necessary in knitting machines, the turning-off means would have to be pressed with a large spring force against the thread. A large spring force is, however, undesired during this turning off, since the spring force acts directly against the thread tension, which in turn is supposed to be held as small as possible.
It is therefore not advantageous to use a conventional thread-delivery device, as shwon in German AS No. 1,585,298, in which the turning-off arm moves the thread out from between the belt and thread-guiding roller and thereby operates a switching-off means, which switches on only a signalling lamp, while after a substantial further swivel path a second switch is operated, which turns off the machine. This has been used in a circular knitting machine up to now only so as to be able to differentiate between overfeeding to a system and breakage. In the first case only a warning indication is given, in the second case stopping takes place.
The purpose of the invention is to construct a device of the above-described type such that, with simple means and slight tension effect at the thread both during paying out of the thread and also during thread breakage, the thread delivery can be interrupted quickly.
In the inventive device a tension change in the unwinding thread influences directly only the swivel arm, the swivel movements of which are converted into naturally quick electrical switching operations. The first switching operation occurs already during a small angular movement and causes, through the switch and electromagnet, a sudden interruption in the thread delivery. This quick reaction is desired for the normal thread change during the operation of the knitting machine. It has the further advantage that is immediately noticed at the thread feeler whether, in spite of the stopped delivery, the tension drops further, thus a thread breakage exists. Since the swivel movement into the switching-off position is quickly started, and on the other hand the thread delivery is interrupted prior to the switching off of the machine, there is so much time available for the second swivel path that the pretension of the swivel arm can be kept small, as is favorable for low thread tension. The return force which engages, directly or indirectly, the thread control element through the electromagnet for interrupting the thread delivery can, however, be of any desired size and thus can be designed to act quickly since it has no influence on the thread tension.
Particularly, it is possible to quickly interrupt the thread delivery by the swivel arm resting during the thread delivery on the first switch and closing the circuit of the electromagnet, and interrupting the circuit at the start of the swivel movement. With this the thread delivery is interrupted immediately, even in the case of a small tension drop.
The electromagnet can engage, in a simple manner when the circuit is closed, the thread-control element against the force of a spring which loads the thread-control element in the direction of the delivery-belt-free area. The speed, with which the thread delivery is interrupted, is thus determined by the stored spring force, which is not limited by having to pay attention to the thread tension. The thread-control element is moved instantaneously when the thread tension starts to drop and the swivel arm accordingly starts to swivel.
In a preferred embodiment the swivel arm is connected to a rotatable and eccentrically spring-loaded disk and a short lever arm is arranged on same, which lever arm carries a contact piece at its free end. The angular movements of the swivel arm can thus be translated into short switching paths of the contact piece. The switches and the associated circuits are stored in a small space. This is particularly important for thread-delivery devices on knitting machines since each knitting system of the machine must have associated with it several thread-delivery devices for the different threads which are to be used alternately.
These several thread-delivery devices and associated thread-control elements can be supported advantageously with their thread-breakage monitor on a common support frame.
The electric connection between the electromagnet which is arrranged on the thread-control elements and the switches can be carried out in an advantageously simple manner by the thread-control elements being arranged elevationally movably on a common support rail which projects out from the support frame and the circuits of the associated electromagnets extend along this support rail.
Further details and advantages of the invention can be taken from the description of one exemplary embodiment, which is illustrated in the single FIGURE of the drawing.